California's energy storage requirement may revolutionize the grid

The spring of 2011 was wetter than usual in the Pacific Northwest. A huge snow year was followed by rain, and during the peak runoff water was ripping through the hydroelectric turbines on Bonneville Power Administration’s dams. Spring is also the windy season, and hundreds of new turbines in the region were also pumping juice into the electrical grid. Even when substantial electricity exports to California were taken into account, the combined wind and hydro-power plants were generating more carbon-free electricity than the region’s residents and businesses could consume.

But too much of a good thing is, well, too much. In order to keep the grid from being overloaded, BPA forced the wind farms to shut down, bashing their bottom line. Controversy and lawsuits ensued: Both wind farmers and salmon advocates would have preferred it if BPA spilled the water over the dams, rather than run it through the turbines.

Regardless of who’s right in this case, the whole brouhaha could have been avoided and the dams and turbines could have continued to pump out power had one piece of technology been introduced: A giant battery. Charge it up during times of oversupply, and draw from it during times of need. If only it were that easy. Thanks to the high cost and still immature technology, large-scale energy storage remains rare in the North American Grid.

If you could just hook a giant battery up to wind turbines and solar panels, it would solve a lot of problems. Photo illustration by Jonathan Thompson.

Earlier this month, however, California’s utility regulators shook the battery world up: They required the state’s biggest utilities – Pacific Gas & Electric, Southern California Edison and San Diego Gas & Electric – collectively to install 1,325 megawatts* of energy storage by the end of 2024. While that’s only about the same capacity as one large coal power plant, it will be a huge leap. Today’s biggest storage projects are only around 140 megawatts, and the largest battery project in California is a mere four megawatts.

Electricity is a crazy product. Just about any other good can be manufactured, stored and then distributed to the consumer according to demand. But electricity is cranked out of turbines or solar panels and sent to consumers at the speed of light. At any given moment, production must be equal to demand, lest the whole grid go haywire and outages ensue – thus the Northwest wind shutdown of 2011. Solar panels only generate significant amounts of power for a limited time each day, and their peak output tends to occur a few hours earlier than peak demand. A big thunderhead blocking the sun's rays from a solar array can cut the array's output by as much as 80 percent in seconds. Wind, meanwhile, tends to blow mostly at night, when demand is low, and second-to-second fluctuations can cause a wind farm’s output to vary dramatically.

That means that for every added megawatt of wind or solar in a particular section of the grid, the operators of that grid have to have on hand a controllable, more predictable power source – usually either hydroelectric or fossil fuel – to smooth the bobbles and back things up in case of dramatic drops in generation. But large scale storage could also play the backup and smoothing role, thereby displacing fossil fuels in the grid. Indeed, without it, the hope of a fossil fuel-free grid is no more than a pipe dream.

Wind and solar resources can fluctuate dramatically over a day, as shown here by a typical 24-hour energy mix on the California Independent System Operator's grid. Source: CAISO.

At a recent gathering of the Rocky Mountain Association of Energy Engineers in Denver, the importance of storage was clear. Several people mentioned the significance of California’s new requirement. And the first ever Randy Udall scholarship, announced at the conference, went to University of Colorado Boulder doctoral student Michelle Lim for her work on energy storage. Robert Welch, a prominent energy consultant, pointed out that energy storage isn’t a totally new idea: When a utility stockpiles coal, it’s storing energy.

Unfortunately, it’s not quite that easy with actual electricity. You can’t just pile it up in a warehouse. Having said that, there is no shortage of storage technologies – though many are untested or costly – from which the California utilities can choose to fulfill the mandate. Just a few examples:

Batteries/chemical storage:

Near San Jose, Calif., the brand new Yerba Buena sodium sulfur battery system has a capacity of 4 megawatts, and will be able to keep a more constant supply of power flowing into Silicon Valley. But batteries are expensive, take a while to charge and the charge doesn’t last a long time – they are the Achilles heel of electric vehicles, too.

Crowdsourcing storage:

One electric car battery isn’t going to do much aside from power the car for 100 miles, but 100,000 of them, all hooked into the grid at the same time, could provide large-scale backup. It’s a serious proposal, and makes sense. The only problem is timing. How do you ensure that an adequate number of folks will have their cars plugged in when you need to draw from their batteries for backup?

Pumped hydro storage:

A reservoir with hydropower is essentially a giant battery, though we can’t control the charging process. Put a reservoir on a hill, pump water up to it during times of high power production, and release the water to turn a turbine during high demand, and you’re getting somewhere. Not a bad idea, and there are several scattered across the U.S., but they require specific topographic conditions.

Thermal storage:

In Gila Bend, Ariz., the Solana solar project reflects sunlight onto tubes, creating heat and steam, which turns turbines that generate electricity. In the process, the sun also heats up salt, which retains the heat, which is later released to generate steam and power when the sun’s not shining.

Compressed air:

Not unlike pumped hydro storage, excess power is used to pump air into underground chambers, where it is pressurized. It can later be released to turn turbines and generate electricity.

And there are many more, including flywheels, superconducting magnetic energy and filling and emptying giant, hollow spheres that hang from offshore wind facilities in order to turn a turbine.

None of these technologies are perfect, and some remain infeasible at a large scale. But then, a decade ago, the same could be said for large-scale wind and solar. As states started requiring utilities to add set percentages of renewable energy to their portfolios, however, innovation accelerated and costs came down. California’s new requirement has the power to do the same with energy storage. If other states follow, as is often the case, it will provide the push needed to bring those big batteries online, and finally loosen fossil fuels’ grip on our electrical grid.

An earlier version of this story said that California utility regulators required the state's biggest utilities to install 1,325 megawatts of "energy storage capacity," but was changed to say "energy storage," for clarity. The following footnote has also been added for clarification.

* "Where MW represents the peak power capacity of the storage resource in terms of the maximum discharge rate." – From the California Public Utility Commission draft decision documents.

Jonathan Thompson is a senior editor at High Country News. Follow him on Twitter @jonnypeace.